Composite titanium dioxide-metal oxide pigment



March 2, 1948.

A. PECHUKAS 2,437,171

COMPOSITE TITANIUM DIOXIDE-METAL OXIDE PIGMEN'I' I Filed Nov. 10, 1943 2 Sheets-Sheet l F'Ki-l FIG I! INVENTOR. ALPH ONSE Psc HU ms Mam}! 1948. A. PECHUKAS COMPOSITE TITANIUM DIOXIDE-METAL OXIDE PIGMEN'I' W Z y/////////// INVENTOR. Q ALPHONSE PEcHuKAs BY BQQWQA W chloride.

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Patented Mar. 2, 1948 COMPOSITE TITANIUM DIOXIDE-MET OXIDE PIGMENT Alphonse Pechukas, Akron, Ohio,

Pittsburgh Plate Glass Company,

assignor to Pittsburgh,

Pa., a corporation of Pennsylvania Application November 10, 1943, Serial No. 509,103 4 Claims. (01. 106-300) This invention relates'to a method of prepar ing modified titanium dioxide pigments. More specifically it relates to pigments which contain small amounts of the oxides of other metals uniformly dispersed therein.

one object of this invention is to provide a method of preparing a mixed pigment of a more uniform composition than can be obtained by milling the pigments in desired proportions. A further object is to provide a method of preparing titanium dioxide pigments containing very small amounts of modifying agents such as aluminum oxide or colored pigments such as chromic oxide.

Application Serial No. 405,418 issued on April 25, 1944, as U. S. Letters Patent 2,347,496 to Irving E. Muskat and myself jointly describes and claims methods of preparing mixed pigments of titanium dioxide and an oxide of chromium by the thermal decomposition of mixtures of titanium tetrachloride and chromic chloride. I have invented a simple and convenient method of pre-' paring similar titanium dioxide pigments contalning minor proportions of admixed oxides of other metals. The method contemplates generally the step of passing hot vaporized titanium tetrachloride in contact with the metallic oxide which is desired as the modifying agent in the mixed pigment. In the presence of hot titanium tetrachloride the oxides are chlorinated, vaporized, and homogeneously dispersed in the titanium tetrachloride. Subsequently, the mixed halides are decomposed by contacting with oxygen and filtered from the gas stream. The final product may be calcined in the usual manner to eliminate traces of chlorine.

Titanium tetrachloride vapors useful in this process may be prepared by the chlorination of titanium ores in the presence of carbon. The crude vapors so produced may contain residual chlorine which is not entirely removed by the procedures used to remove iron chloride, for example by washing with liquid titanium tetra- The excess chlorine content of the gaseous chlorination product will assist the chlo- 1 rination of the modifying agent and permit the reaction at a lower temperature than would j otherwise be possible.

By my new method very intimate mixtures of titanium dioxide with other modifying oxides may be obtained. Silicon dioxide,'zinc oxide, aluminum oxide may be added to improve the color oil absorption, particle size, chalking characteristics and other essential physical and chemical properties of the pigment. Other oxides such as lead oxide, chromic oxide, and iron oxide 2 may be added to produce tinted pigments. Similarly the colors may be blended by using two or more colored oxides in suitable proportions.

A preferred modification of the invention is demonstrated by Figure I of the accompanying drawings. A conduit l conducting the titanium tetrachloride from a vaporizer or from a chlorination furnace is shown leading into the preliminary reactor 2 which has a substantially increased cross-section area for the purpose of reducing the linear velocity of the gas. The titanium tetrachloride then passes through a porous bed 3 containing the metal oxide which is used to modify the final pigment. The porous bed may be comprised of large granules of the metal oxide or it may contain a small proportion of metal oxide suspended on a carrier of porcelain, coke, asbestos, or other inert material which will provide ample interstices to facilitate the passage of the gas stream. A perforated diaphragm 4 supports the porous bed., The reactor should be provided with a charging door 5 suitable for withdrawing the residue or spent charge. In passing through the porous body containing metal oxide the titanium tetrachloride at proper temperatures will react with the metal oxide and produce the corresponding chloride. The gas stream entering must necessarily be at a temperature which will enable the chlorination to proceed. Accordingly, it may be necessary to preheat the gas stream or to heat the preliminary reactor by suitable heating elements 6, especially when oxides having less volatile chlorides, such as chromium chloride, zinc chloride and lead chloride, are used..

The mixed chloride vapors are then drawn ofi through conduit 1 and passed into furnace H) where they are mixed with oxygen or an oxygen containing gas. The oxygen stream must be so directed that the entire reaction is conducted out of contact with the furnace walls in order to avoid the formation of macrocrystalline titanium dioxide particles, The air or oxygen may be introduced in parallel flow at H or in countercurrent flow at I2. Frequently, it is desirable to introduce part or the. air at each of sources I I and [2. The reaction in zone It! produces titanium dioxide by the equation:

into furnace 26 where it may be heated by means of suitable heating elements 24. The gas then passes upwardly through a perforated diaphragm and into the pervious bed of. material 25 which;

contains the oxide of the element which is; re-

quired to produce the desired modified pigment,

Further heating elements 24- are provided adjacent the oxide bed to enable the formation and evaporation of the desired quantity of the modifying cnstituent.. The mixed halide stream is. passed; into conduit, Zland then to the decomposition furnace whicnis notshown.

Fig. III shows a crosssectiondiagram of a decomposition furnace l8- modified to prevent the decomposition of titanium tetrachloride in contact with the hot inlet-tube. B the. use of. this apparatus the vaporized halide stream in conduit l i is mixed with sufficient air from inlet [5. so that themixture in tube [6 will'exist at a temperature less than that required for the. decomposition. Generally a temperature'below 600 C. will be suitable. A second source. of air i1 is preheated to a. temperature which will cause the decomposition when the streams of reactants are mixed in furnacechamberw. Preferably temperaturesgreater than 700C. are used for the decomposition.

Another means of preventing theformation of macro-crystalline pigments is shown in Figs. I and II. The. end of conduit 1 is. enclosed by a porous cup. 8 ofunglazed porcelainor other pervious material. The cup is provided with an opening 9 at the center of the endface and is made. of such composition. andthickness that to percentof thetitaniumtetrachloride passes.

through the porous wallwhi1e85 to. 95 percent passes. through the opening 9. By this mechanism the atmosphere outside the..porous cup is,

diluted. with the. reactants. andreaction products which sweep theoxy cnaway from openingii.

Thus, no, coarse crystalline titanium. dioxide is. formed by contactv of the. hot] tube with the reacting gases.

Further details of the processalie ,set forth in the following specific examples:

Example I Apparatus constructed in accordance with Fig ure I was used to prepare titanium dioxide pigment. Chromic oxide in coarse granular form was placed inthe preliminary reactor. Titanium tetrachloride at 700 C. was, passed through the chromicoXide bed maintainedat a temperature of 755 to 785 C. by meansof-heating elements in the furnace wall. The decomposition was conducted at about 900 C. by introducing-preheated A stream of vaporized;

air in parallel flow. The reaction products were drawn 01f through a filter. A light green pigment containing 1.3 percent chromic oxide was obtained.

Example II A mixture of titanium tetrachloride and aluminum chloride-vaporsvwas. produced using apparatus similar to that shown in Figure III. Granular aluminum oxide was placed within the furnace which was maintained at 675 C. by means, of electric heating means located in the furnace walls. The vapor mixture contained approximately 2.5 percent aluminum chloride.

The mixed chloride vapors were passed into a decomposition furnace provided with a source of preheated air-as in Figure III and provided with a means for introducing air into the vapor inlet tube. The preheated air entered the furnace at above 1200 C. and when contacted with the halide vapors producedcomplete decomposition. The reaction; took-place at a; temperature of 850 to 900 C. The suspension of-titanium dioxide in fixed gaseousproductswas-v filtered to yield, a

stable T102; pigment containing 3J7 percent of alumina.

Although the invention has been. described with respect to, certain specific embodiments, the details thereotshalinot-be construed as limitations on theiscope of the claims except as defined ;by the following claims.

Iclaim:

l. The method of preparing atitanium dioxide pigment which comprises pafifing vaporized titanium tetrachloride through a porous mass of an oxide of another metal which oxide is susceptible of undergoing chlorination upon contact with titanium tetrachloride; maintaining the vapor temperature sufficiently highto form and vapori'ze a chloride of said metal, permitting only a portion of' the titanium tetrachloride to react withthe oxide whereby to form axvapor mixture of theresulting metal chloride. and titanium tetrachloride, removing the mixture from the porous mass and thermally. reacting the vapor mixture with oxygen to convert the chlorides therein to oxides,

2. A method as defined in claim 1 in which the oxide is aluminum oxide.

3. A method as defined in claim 1 in which the oxide is an oxide of chromium.

4. A method as defined in claim 1 in which the oxide is silicon dioxide.

ALPHONSE PECHUKAS.

REFERENCES CITED 1927, vol. VII, page 82, linesl and 2.

(Copy in Division 59.) 

